This invention relates, in general, to electronics, and more particularly, to capacitive devices and methods of manufacture.
Capacitance tuning devices or variable capacitors are used in wireless Radio Frequency (RF) and microwave Integrated Circuits (ICs) for many telecommunication applications. RF and microwave ICs include Voltage-Controlled Oscillators (VCOs), impedance matching circuits, adjustable RF amplifiers, filter tuning circuits, antenna tuning circuits, crystal trimming circuits, and many others. These RF and microwave ICs typically use PN junction semiconductor variable capacitors, commonly referred to as varactor diodes, off-chip mechanically trimmable capacitors, or micro-electromechanical systems (MEMS) variable capacitors.
However, the varactor diodes cannot meet the high speed requirements of the RF and microwave circuits because of the excessive series loss or low quality factor of the varactor diodes. Furthermore, the varactor diodes also cannot meet the wideband wireless communication requirements because of the narrow capacitance tuning range of the varactor diodes. Current wideband frequencies range from approximately 800 MegaHertz (MHz) to 2.5 GigaHertz (GHz). Similarly, the off-chip mechanically trimmable capacitors also have disadvantages including increased cost, increased component size, and reduced reliability. Additionally, the MEMS variable capacitors also have drawbacks including the lack of RF isolation, the lack of direct current (DC) and alternating current (AC) isolation, sensitivity to micro-phonics, sensitivity to electrical disturbances, sensitivity to temperature changes, and many others.
Accordingly, a need exists for a capacitive device and a method of manufacturing that is compatible with RF and microwave IC applications and that can also satisfy wideband communication requirements.